1. The Field of the Invention
The present invention relates to heat dissipation systems that use forced air or other type of gas flowing over the surface of an object to remove heat from the object. The present invention also relates to heat dissipation systems that use ducted flow of air or other type of gas to remove heat from an object.
2. The Relevant Technology
As shown in FIG. 1, when a gas 100, such as air, flows over a smooth surface 102, the velocity of the gas near the surface 102 is less than the velocity of the free stream 104. This creates a layer of lower velocity gas, known as a viscous boundary layer 106, near surface 102. The thickness of the viscous boundary layer 106 is defined by the point 108 where the gas velocity is 99% of the free stream velocity. Because of the lower gas velocity, less heat transfer can take place between a hot surface 102 and the gas 100, thus reducing the heat exchange efficiency. As a result, there is also a layer of higher temperature gas that is formed that is known as a thermal boundary layer 110. The thickness of the thermal boundary layer 110 is defined by the point 112 where the temperature of the gas is 99% of what it would be for the free stream flow 104. The thickness of the thermal boundary layer 110 may or may not coincide with the thickness of the viscous boundary layer 106.
From the foregoing discussion, it is obvious that the thinner the thermal boundary layer 110, the steeper the temperature gradient and thus the greater the heat transfer rate. Thus, there are various approaches that have been taken to attempt to reduce the thermal boundary layer 110 to increase heat transfer.
In one approach, the thermal boundary layer 110 is disrupted or destabilized by patterning the surface with crests, dimples, or depressions. The patterning produces eddies or vortices on the surface, which provide more turbulent flow, thereby minimizing the thermal boundary layer that has formed on the surface. However, the eddy or vortex flows have their own local boundary layers with a corresponding reduction in local heat exchange efficiency. As such, while the patterned surface yields a better overall heat exchange efficiency than a smooth surface, the efficiency is not as high as it could be due to the local boundary layers.
Accordingly, what is needed are heat dissipation systems that not only minimize the surface boundary layer to increase heat exchange efficiency, but also minimize the local boundary layers so as to increase the local heat exchange efficiency, thereby providing more efficient and greater overall heat exchange capabilities.